1. Field of the Invention
The present invention relates to a compact zoom lens system having a high zoom ratio (up to about 10) ranging from a wide field angle to a telephoto angle. The zoom lens system of the present invention is especially suitable for use in a still camera.
2. Description of the Related Art
One type of conventional zoom lens system ranging to a wide field angle is constructed by two lens groups: a negative front lens group and a positive rear lens group. When the zoom ratio is increased in this two lens group type, the shifting amount of the rear lens group will be very large, which practically limits the zoom ratio of this type up to about 2-2.5.
An improvement of the above-mentioned two lens group type is a four lens group type, in which the rear lens group of the former type is divided into three lens groups, consisting of negative-positive-negative-positive lens groups. The zoom ratio is expanded up to 3-4 with this type, but the market demand these days is for a still higher zoom ratio. It is well known that as the zoom ratio becomes higher, the zooming function is promoted but the aberrations will deteriorate and the size of the zoom lens system will grow larger.
Many zoom lens systems have been proposed so far (some of them are described in the U.S. Pat. Nos. 4,494,828; 4,666,257; 4,673,258; 4,701,033; 4,789,229; 4,896,950; and the Japanese Published Unexamined Patent Application Nos. S57-192917, S61-212814, S63-208015, H1-178912, H1-197713, H1-223409, H1-252915) but non has been successful in achieving a compact zoom lens system having a high zoom ratio ranging to a wide field angle.